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● VLT Proxy Gateway enables one VLT domain to act as the default gateway for its peer VLT domain in an eVLT topology.
Configure Virtual Link Trunking
VLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLT interconnect on both
peer switches.
Important Points to Remember
● You cannot enable stacking simultaneously with VLT. If you enable both at the same time, unexpected behavior can occur.
● VLT port channel interfaces must be switch ports.
● If you include RSTP on the system, configure it before VLT. Refer to Configure Rapid Spanning Tree.
● If you include PVST on the system, configure it before VLT. Refer to PVST Configuration.
● Dell EMC Networking strongly recommends that the VLTi (VLT interconnect) be a static LAG and that you disable LACP on
the VLTi.
● Ensure that the spanning tree root bridge is at the Aggregation layer. Refer to RSTP and VLT for guidelines to avoid traffic
loss, if you enable RSTP on the VLT device.
● If you reboot both VLT peers in BMP mode with static VLT LAGs, the DHCP server reply to the DHCP discover offer may
not be forwarded by the ToR to the correct node. To avoid this issue, configure the VLT LAGs to the ToR and the ToR port
channel to the VLT peers with LACP.
● If supported by the ToR, enable the lacp-ungroup feature on the ToR using the lacp ungroup member-independent
port-channel command. If the lacp-ungroup feature is not supported on the ToR, reboot the VLT peers one at a time.
After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity.
● When a VLAN is created on VLTi peers, the VLTi port-channel is added automatically to the VLAN, whether the vlan
have members or not. A VLAN creation or deletion message from the VLT peer is the trigger for adding or removing
VLTi port-channels to or from a VLAN. You can manually add or remove a VLTi port-channel to a VLAN. In case a VLTi
port-channel is manually removed from a VLAN, it is added back to the VLAN after reload of the VLTi peers.
● Use the lacp ungroup member-independent command only if the system connects to nodes using bare metal
provisioning (BMP) to upgrade or boot from the network. Otherwise, when the member links flap, the links become
independent switch ports and forward the traffic even before LACP is formed on that port.
● Ensure that you configure all port channels as hybrid ports and as untagged members of a VLAN where the LACP ungroup
option is applicable.
● BMP uses untagged dynamic host configuration protocol (DHCP) packets to communicate with the DHCP server.
● o disable this feature on VLT and port channels, use no lacp ungroup member-independent {vlt | port-
channel} command under the configuration mode.
● When you enable IGMP snooping on the VLT peers, ensure the value of the delay-restore command is not less than the
query interval.
● When you enable Layer 3 routing protocols on VLT peers, make sure the delay-restore timer is set to a value that allows
sufficient time for all routes to establish adjacency and exchange all the L3 routes between the VLT peers before you enable
the VLT ports.
● Only use the lacp ungroup member-independent command if the system connects to nodes using bare metal
provisioning (BMP) to upgrade or boot from the network.
● Ensure that you configure all port channels where LACP ungroup is applicable as hybrid ports and as untagged members of a
VLAN. BMP uses untagged dynamic host configuration protocol (DHCP) packets to communicate with the DHCP server.
● If the DHCP server is located on the ToR and the VLTi (ICL) is down due to a failed link when a VLT node is rebooted in
BMP mode, it is not able to reach the DHCP server, resulting in BMP failure.
● If the source is connected to an orphan (non-spanned, non-VLT) port in a VLT peer, the receiver is connected to a VLT
(spanned) port-channel, and the VLT port-channel link between the VLT peer connected to the source and ToR is down,
traffic is duplicated due to route inconsistency between peers. To avoid this scenario, Dell EMC Networking recommends
configuring both the source and the receiver on a spanned VLT VLAN.
● Bulk Sync happens only for Global IPv6 Neighbors; Link-local neighbor entries are not synced.
● If all of the following conditions are true, MAC addresses may not be synced correctly:
○ VLT peers use VLT interconnect (VLTi)
○ Sticky MAC is enabled on an orphan port in the primary or secondary peer
○ MACs are currently inactive
If this scenario occurs, use the clear mac-address-table sticky all command on the primary or secondary peer
to correctly sync the MAC addresses.
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Virtual Link Trunking (VLT)